1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly to an apparatus for testing a liquid crystal display device and testing method which is suitable for a large size liquid crystal display device and can reduce a testing time.
2. Description of the Related Art
The growth in demand for various portable electronic devices, such as mobile phones, personal digital assistants (PDAs), and notebook computers has increased the demand for light weight, thin profile, small flat panel display devices. Such flat panel display devices include liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and vacuum fluorescent display (VFD) devices. Of these different devices, the LCD devices are actively developed due to their simple mass-production techniques, their easy driving systems, and high picture quality.
The LCD device includes a lower substrate, an upper substrate and a liquid crystal layer formed between these two substrates. The lower substrate is a driving device array substrate, and includes a plurality of pixels. A driving device such as a thin film transistor is formed at each pixel. An upper substrate is a color filter substrate, and includes a color filter layer for implementing actual colors. In addition, a pixel electrode and a common electrode are formed on the lower substrate and the upper substrate, respectively, and an alignment film for aligning liquid crystal molecules is applied on the pixel electrode and the common electrode.
The lower substrate and the upper substrate are attached together by a sealant formed along an outer edge of the substrate. Spacers formed between the upper substrate and the lower substrate maintain a uniform cell gap. Liquid crystal molecules are driven by a driving device formed on the lower substrate, wherein the quantity of light transmitted through the liquid crystal layer is controlled to display an image.
In the LCD device having such a structure, the lower substrate is formed by a driving device array substrate process for forming a driving device, and the upper substrate is formed by a color filter substrate process for forming a color filter.
In the driving device array substrate process, a plurality of gate lines and a plurality of data lines arranged on the lower substrate that cross to define pixel regions are formed. A thin film transistor, a driving device connected to the gate lines and the data lines, is formed at each pixel region, and then a pixel electrode connected to the thin film transistor is formed to drive the liquid crystal layer when a signal is applied thereto through the thin film transistor.
In addition, in the color filter substrate process, a black matrix is formed on the upper substrate, then a color filter is formed thereon, and finally a common electrode is formed thereafter.
Thereafter, the two substrates are attached together by a spacer and sealant forming process, and then the attached substrates are cut into panel units thereby completing a liquid crystal display panel.
Before the two substrates are attached, a testing process is additionally carried out to detect defects such as a short or open circuit of the thin film transistor and between lines formed on a thin film transistor (TFT) array substrate.
FIG. 1 is a schematic view illustrating a method for testing a TFT array substrate.
As shown, an apparatus 1 for testing the TFT array substrate includes a TFT array substrate 10 to be tested; a modulator 35 installed above the TFT array substrate 10; and a camera 40 installed above the modulator 35.
The modulator 35 includes Polymer Dispersed Liquid Crystal (PDLC 30) layer injected between a substrate 20 on which a transparent electrode 31 is formed and a reflecting plate 33. The PDLC layer 30 is formed of liquid crystal drops obtained by mixing liquid crystal with polymer and then separating the liquid crystal from the polymer by emitting ultraviolet rays to the mixture. The PDLC layer 30 is made of an epoxy resin containing a resin and a hardener. The PDLC layer 30 is driven by a voltage difference between the transparent electrode 31 formed on the substrate 20 of the modulator 35 and the pixel electrode 11 formed on the TFT array substrate 10.
If a voltage is not applied to the PDLC layer 30, liquid crystal drops are randomly arranged, thereby diffusing incident light. Thus, a dark image is observed in the camera 40. In contrast, if a voltage is applied to the transparent electrode 31 and the pixel electrode 11, the liquid crystal molecules in the liquid crystal drops of the PDLC layer 30 are arranged parallel to an electric field to thereby reflect incident light with a reflecting plate 33 and transmit the reflected light. Thus, a bright image is observed in the camera 40. Accordingly, the brightness of an image displayed from the camera is observed by changing the voltage between the pixel electrode 11 formed on the TFT array substrate 10 and the transparent electrode 31 formed at the modulator 30.
When a defect such as an open or short circuit occurs at the TFT array substrate 10, the brightness of an image in that region as observed through the camera becomes different from that of another region, making the defect easily detected.
However, the related art apparatus for testing the TFT array substrate having such a structure has a number of problems, including the following.
First, because the modulator 35 used for an existing testing apparatus has a reflection plate formed by alternately laminating TiO2 and SiO2, manufacturing a large size modulator is difficult. Accordingly, to test an entire surface of the TFT array substrate, the test has to be repetitively carried out with the modulation moved. For this reason, the test takes a long time to complete and the modulator is not suitable for a large size liquid crystal display device.
In addition, the modulator 35 maintains a distance of approximately 10˜20 μm from the TFT array substrate 10. When using an organic passivation layer to secure an aperture ratio in a TFT array substrate 10 process, a protrusion may be formed at the substrate's surface. If the reflecting plate of the modulator comes in contact with the protrusion, the reflecting plate is torn. Accordingly, the modulator has to be replaced with new one, thereby increasing cost.